Installations for reprocessing irradiated nuclear fuels have what are referred to as large-area hot cells for accommodating the process components. The process components are set up in supports or structures known as racks within the large-area radiation-shielded cells.
Maintenance operations within the large-area radiation-charged cell should be carried out as far as possible without the necessity of operating personnel entering the cell. Accordingly, it has been proposed that maintenance operations should be carried out by portable remote-handling machines.
It has previously been suggested that manipulator carrier systems should be provided which act in the horizontal direction from a central path of the hot cell on the process components. A manipulator carrier system of that kind affords the possibility of using electrical servo and power manipulators as well as robots and programmable devices.
The use of a robot in the radioactively loaded cell hitherto involved difficulties because the angle encoding means thereof failed under the effects of the radioactivity. Angle encoding means detect the information signals by way of optical image patterns. Angle encoding means of that kind cannot operate effectively in the field of radiation because the semiconductor components are affected by the radiation and can therefore produce faulty information.
It has therefore already been proposed that, instead of the angle encoding means, resolvers should be used as rotary sensors which provide for electromagnetic pulse counting. The information signals are then obtained by induction. The resolver is at a defined zero point at the beginning of the counter operation.
Resolvers induce information signals in a coil, and such information signals, after a counting operation, identify the position of the associated moved robot joint arm. In this connection, reference can be made to published German patent application DE-OS No. 24 28 573. However, when, for example, a robot is in the switched-off condition, there may be a change in the position of the corresponding joint arm because of the force of gravity pulling the arm downwardly. In the switched-off condition, the joint arm then changes from the position which was last detected and which remains stored in the computer as the actual position thereof. Now, after the robot is switched on, the position of the joint arm is different from that which is known to the computer. The resolver and the counter are no longer matched to the zero point of the joint arm. A counting operation now produces faulty information and not the actual position or location of the joint arm.
This disadvantageous displacement of the robot joint arm relative to the zero counting point, once it has been set, can also occur during operation.
German published and examined patent application DE-AS No. 24 42 865 discloses an arrangement wherein the accuracy of adjustment thereof is independent of load and wear. This arrangement has a disc which carries abutments and which is non-rotatably but axially displaceably mounted. A robot is disclosed in German published patent application DE-OS 28 31 361 which is equipped with return means fitted with two abutments. The abutments represent a defined rest position.
Also, published German patent application DE-OS No. 30 45 984 discloses a programmable manipulator.